fl parsing is sensitive to newlines at the end of field names

Details

Description

As reported by giovanni.bricconi on the user list, there is a bug in "fl" parsing that causes solr to get confused when a field name is followed by a newline character – eg: in a requestHandler default like...

...this results in solr assuming it should use function parsing to evaluate the field name, which can cause missleading errors if the field name can't be used in a function (eg: "can not use FieldCache on multivalued field: store_slug")